Conventionally, a liquid crystal display device has been used in various electronic devices such as a television set, a laptop PC (Personal Computer), a desktop PC, a PDA (Personal Digital Assistant: a mobile terminal), and a mobile phone. This is because the liquid crystal display device has the following advantages: (i) it is thinner and lighter than a CRT (Cathode Ray Tube)-based display and (ii) it can be driven at a low voltage, and (iii) it can realize lower power consumption.
A liquid crystal display device in which TFT (Thin Film Transistor) elements are used (a TFT liquid crystal display device) realizes a high display quality since all pixels are switched via respective TFT elements.
Meanwhile, it is rapidly becoming popular to display a moving picture by use of a liquid crystal display device in a television receiver or the like. In view of the circumstances, it is necessary to further increase a response speed of a liquid crystal display panel in the liquid crystal display device so that a moving picture can be finely displayed.
Against a backdrop of this, it is a liquid crystal display device having an OCB (Optically Self-Compensated Birefringence type) liquid crystal display panel that has recently gained particular public attention. The liquid crystal display device having the OCB liquid crystal display panel is generally arranged as follows: Liquid crystal molecules are provided between two substrates each of which is subjected to an alignment treatment which causes the liquid crystal molecules to be aligned in parallel to each other and in an identical direction. Wave plates are provided on respective surfaces of the two substrates. Polarizing plates are further provided on the respective two substrates so as to be in a crossed Nicols relationship between the polarizing plates.
(Reverse Transition)
For example, assume that the OCB liquid crystal display panel is used in a normally white mode (hereinafter referred to as an NW mode) in which a black display is carried out during high voltage application and a white display is carried out during low voltage application. In order to realize a white display having a high transmittance, it is necessary to apply a voltage to a liquid crystal layer, which is substantially reduced to a critical voltage (Vcr) at which a transition occurs from a splay alignment to a bend alignment (a splay-to-bend alignment).
Therefore, a transition may occur, during a white display, from the bend alignment to the splay alignment (a bend-to-splay transition) (hereinafter referred to as a reverse transition) in which a splay alignment state of liquid crystal molecules that has been once changed to a bend alignment state is reversed to the splay alignment again. This causes prevention of an appropriate display.
The reverse transition also occurs in a case where a liquid crystal display device is driven by a voltage which is not less than the critical voltage (Vcr). In case of a TFT liquid crystal display device, the reverse transition may occur in a gap between respective pixel electrodes provided above both a gate bus line and a source bus line. In such a case, a splay alignment region of the bus line and a splay alignment region of the source bus line are easy to be combined.
In such a state, the splay alignment region may intrude into a display region during a white display. This will cause a display defect.
(High White Voltage)
Various methods for preventing the reverse transition have been suggested.
For example, a method has been suggested in which a voltage (hereinafter referred to as a white voltage) applied during a white display in the normally white mode is sufficiently higher than the critical voltage (Vcr).
However, according to the method in which the white voltage is increased, it is difficult to realize a high-brightness OCB panel. This is because there is a trade-off between an increased white voltage and a brightness.
(Black Insertion)
Note that, for preventing the reverse transition, another method has been suggested in which a signal for preventing the reverse transition which signal is different from an image signal is applied.
Specifically, for example, a method has been suggested in which a black display is inserted (a black insertion is carried out) at least one time within one (1) frame of an image display so as to stably retain the bend alignment.
However, the method employing the black insertion has caused a problem of deteriorating a white brightness, which is similar to the method employing the high white voltage.
There has also been a problem that the black insertion causes a flicker.
(Patent Literature 1)
Patent Literature 1 describes an arrangement in which a protruded part is provided, in a circumferential part of a pixel of a plane which is parallel to a substrate plane so that liquid crystal molecules as a whole are efficiently subjected to the transition to the bend alignment. This will be described below with reference to the drawing.
FIG. 14 schematically illustrates a liquid crystal display device 100 described in Patent Literature 1. The liquid crystal display device 100 described in Patent Literature 1 includes a plurality of signal electrode lines 106 and a plurality of gate electrode lines 107 which cross at substantially right angles to the plurality of signal electrode lines 107 (see FIG. 14).
Pixel electrodes 102 which are substantially rectangular are provided in respective pixel regions which are substantially defined by the plurality of signal electrode lines 106 and the plurality of gate electrode lines 107. Each of the pixel electrodes 102 is connected to a switching transistor 108, which is provided in a vicinity of each of intersections of the plurality of signal electrode lines 106 and the plurality of gate electrode lines 107.
According to the liquid crystal display device 100 described in Patent Literature 1, a signal electrode line 106 has a protruded part 161. A pixel electrode 102 has a depressed part 121 which is provided so as to correspond to a shape of the protruded part 161 and so as to face the protruded part 161.
The pixel electrode 102 has a protruded part 122 whose shape is similar to that of the protruded part 161 of the signal electrode line 106. A signal electrode line 106 has a depressed part 162 which is provided so as to correspond to a shape of the protruded part 122 and so as to face the protruded part 122.
Patent Literature 1 describes that, according to the arrangement, the liquid crystal molecules as a whole are efficiently subjected to the transition to the bend alignment.
Patent Literature 1
Japanese Patent Application Publication, Tokukai, No. 2002-250942 A (Publication Date: Sep. 6, 2002)